Microwave traveling wave device with electronically switched interaction characteristics

ABSTRACT

A microwave traveling wave device is disclosed with means for selecting and controlling the optimum efficient interaction characteristics between the electron beam and periodic slow wave propagating circuit, particularly in the exchange of energy with the backward wave components of the beam. The device provides in an integral embodiment for pulsed or continuous wave as well as dual mode operation with high and low operating currents. Electronically actuated means to control the electrical and propagation characteristics are incorporated in combination with the electrode structures bounding the interaction region, means for electron beam interception, as well as means for controlling the phase shift of the electromagnetic energy waves on the periodic slow wave circuit. Tunable sideband spurious signals have been measurably reduced in microwave devices employing embodiments of the invention.

United States Patent Appl. No. Filed Patented Assignee MICROWAVE TRAVELING WAVE DEVICE WITH ELECTRONICALLY SWITCHED INTERACTION CHARACTERISTICS 3,302,126 l/l967 Orr 331/82 3,379,990 4/1968 Scharfman 3l5/39.3X 3,400,298 9/1968 Krahn 331/82X Primary Examiner-Herman Karl Saalbach Assistant Examin erSaxfield Chatmon Attorneysl-larold A. Murphy, Joseph D. Pannone and Edgar O. Rost ABSTRACT: A microwave traveling; wave device is disclosed with means for selecting and controlling the optimum efficient interaction characteristics between the electron beam and Clmms9Drawmg Figs' periodic slow wave propagating circuit, particularly in the [LS- exchange of energy the backward wave components of 315/36, 315/393, 331/82, 330/ the beam. The device provides in an integral embodiment for h.-

or continuous wave as we as dual mode operation [50] Field of Search SIS/39.3, i h hi h d low operating currents. Electronically actuated 1- (X) means to control the electrical and propagation charac- 56 R f Cted teristics are incorporated in combination with the electrode 1 e "cums structures bounding the interaction region, means for electron UNITED STATES PATENTS beam interception, as well as means for controlling the phase 2,578,434 12/1951 Lindenblad 330/43X shift of the electromagnetic energy waves on the periodic slow 2,933,638 4/1960 Dench 3l5/39.73X wave circuit. Tunable sideband spurious signals have been ,991 l/ 1963 0sepChuck..... 315/393 measurably reduced in microwave devices employing embodi- 3,253,230 4/1966 Osepchuck 331/82 ments of the invention.

PIN DIODE 68 54 /PIN DIODE 62 60 54 a 64 a L 2 Patented April 6, 1971 3,573,540

2 Sheets-Sheet 1 OUTPUT l0 TERMINATION PRIOR ART PIN DIODE 68 560 54 PIN DIODE 82 /PIN DIODE s2 A 60 540 64 s 5 FIG: 4

I L2 84 86 FIG. 3 '66 82 u [-762 '(WAVELENGTHS) DISTANCE ALONG TUBE L, o 5 l0 l5 0 e m a 5 D t 4 MAx|MuM .n AVERAGE a 3 r MINIMUM LU $4 2 2m lj I M/VE/VTDR 2 5m 46 48 JOHN .M OsEPcHw;

1 ,0 REGION 1'-+P- REGION 2 ---Dl ATTORNEY Patented April 6, 1971 3,573,540

2 Sheets-Sheet 2 OUTPUT TERM I NATION FIG. 6

7 HVVE/VTOI? ZD|5TANCE JOHN M OSEPCHUK NG BE B C77 1 Y (a w L- L 2 ATTORNEY MICROWAVE VELING WAVE DEVICE WITII ELECTRONICALIJT SWITCIIED INTERACTION CIIACTEIIISTICS BACKGROUND OF THE INVENTION Traveling wave electron interaction devices, particularly oscillators for the generation of microwave frequency signals, include periodic slow wave energy propagating circuits such as a delay line coextensive with and spaced from a continuous sole electrode to define therebetween an electron interaction region. Electron beam generation and collecting means are commonly mounted adjacent to the ends of the path provided along the interaction region. In such devices of the M-type a transverse electric field is established between the slow wave structure and the sole electrode. A magnetic field extends orthogonally to the electric field with the combined crossed fields influencing the trajectory of the electron beam. Exchange of energy with high frequency waves propagated along the slow wave circuit will result when the velocity of the beam is synchronized with the phase velocity of the high frequency waves. In one embodiment of an M-type device referred to as a backward wave oscillator the high frequency microwave energy travels in a direction opposite to the general direction of the travel of the electron in the beam. Another device referred to as the O-type provides a magnetic field parallel to the electron beam path which is commonly directed along the tube axis. Other applicable devices include beam type devices which involve an interaction phenomenon with a wave propagated on a slow wave periodic circuit.

In the signal outputs of the devices under consideration spurious unwanted signals of many various types have been observed in the output signals. Such spurious signals are radiated in many ways including transmission through the power supply leads as well as the main output waveguide to the antenna of a radar system. The sources of these spurious signals are manyfold. The known mechanisms include alternate synchronous or cyclotron wave circuits or space charge modes of oscillation, electron beam gun instabilities, harmonics and intermodulation components. Suppression of these spurious oscillations at the source by filtering with reflective or nonreflective means or appropriate adjustment of operating voltages and components have assisted in cleaning up the output signals of oscillators. Ferrite devices coupled in the transmission lines have also assisted in reducing certain of the spurious signals generated. There still remains, however, the sideband spurious signals about which relatively little is understood and which have resisted all attempts of filtering utilizing known techniques. These sideband spurious type signals, particularly when connected with the existence of low frequency signals, are generated substantially close to the carrier frequency and no effective means for suppression has therefore been successful without sacrificing operating performance. Such signals are also closely related to backward wave interaction. The most effective solution now known in the art comprises avoiding the area of performance where sideband spurious signals arise. The practicality of such a solution, however, is questioned since the avoided area is usually the area of highest power or efficiency.

In dual mode operation where the same device is utilized for both pulsed and continuous wave operation the sideband spurious signal problem is a serious problem. An attempt to solve the sideband spurious sigial problem therefore is of paramount importance in present day microwave oscillators including such devices used for dual mode operation.

SUMY OF THE INVENTION In accordance with the teachings of the present invention means are provided for switching between different interaction lengths for generation of oscillations. An active element incorporated within the device will substantially isolate the downstream portion of a periodic slow wave propagating circuit to thereby allow the beam to principally interact and exchange energy over a shorter length of delay line. The

decoupled interaction region will be utilized in another mode of operation simply by deactivating the active switching element. In an illustrative embodiment of the invention a diode switch similar to a PIN diode may be utilized in communication with the slow wave circuit structure. A suitable switching pulse either externally derived or connected through internal electrode structure provides the means for actuating the active spurious control element for adjustment of the interaction length.

Other embodiments include an auxiliary control element for selectively intercepting the electron beam to thereby vary the interaction length also actuated by either internal or external derived voltage source means. In addition, a segmented sole electrode may be provided for adjusting the effective interaction length between the beam and the circuit components. In this embodiment there will be little if any synchronism in the velocities of the beam in the downstream region which renders the first interaction region closest to the cathode element as the frequency determining circuit.

Finally, a diode switched microwave phase shifter is provided at the critical point along the slow wave circuit in order to make use of both interaction regions by appropriately adjusting the phase between the two circuits. Again the respective interaction line lengths are determined for the optimum modes of operation.

BRIEF DESCRIPTION OF THE DRAWINGS The invention, as well as the details of construction of a number of preferred embodiments, will be readily understood after consideration of the following detailed description and reference to the accompanying drawings, in which:

FIG. I is a schematic representation of a prior art crossed field traveling wave device;

FIG. 2 is a graph based on computations of RF energy amplitude as a function of position along a propagating circuit in a traveling wave device;

FIG. 3 is a fragmentary schematic representation of a propagating circuit in an illustrative embodiment of the inventron;

FIG. d is a schematic representation of an alternative propagating structure incorporating semiconductor switching for selection of optimum slow wave circuit lengths;

FIG. 5 is a fragmentary cross-sectional view taken along the line 5-5 in FIG. 4;

FIG. 6 is a schematic representation of an alternative embodiment of the invention involving selective switching of the electron beam means;

FIG. '7 is a schematic representation of still another altemative embodiment of the invention involving a segmented sole electrode circuit;

FIG. d is a schematic representation of an alternative embodiment involving a diode switched microwave phase shifter embodying the principles of the invention; and

FIG. 9 is a graph plotting RF amplitude as a function of the slow wave circuit length with and without the diode switched phase shifting means in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. I a prior art embodiment ofa crossed field traveling wave device is shown utilizing extended interaction between a stream of electrons and a guided electromagnetic wave traveling along a periodic wave retardation circuit. Such devices conventionally include an elongated delay line It illustratively of the interdigital delay line type, having a plurality of elements I2 spaced from a coextensive electrode 114lcommonly referred to as the sole electrode. A DC electric field is established between the delay line and sole electrode with the delay line usually at a positive potential and the sole electrode biased at a negative potential. The delay line and sole electrode are bounding members defining thcrcbetween an interaction region Id. The delay line III which is illustrated for backward wave operation is provided with a high frequency output coupled to terminal 18 adjacent to the electron beam source. The line is terminated by means coupled to terminal 20. For forward wave operation the tenninal connections would be reversed. For amplifier devices an RF input will be fed to either terminal 18 or 20 with the output being coupled to the remaining tenninal.

An electron beam is generated an projected into the interaction region along a substantially linear path by means of an electron gun assembly 22 including a cathode 24 and a grid electrode 26. An accelerating electrode 28 focuses the electron beam along the desired trajectory and is usually maintained at a positive potential with respect to the cathode by means of voltage source 30. Grid electrode member 26 is generally negatively biased with respect to cathode 24 by means of a suitable voltage source 32.

Sole electrode 14 is suitably biased at a negative potential with respect to the delay line by voltage source 34. A magnetic field is established in the interaction region normal to the electric field as represented by the circles 36 having crosses therein to indicate the field direction. Any suitable means such as a permanent magnet or electromagnet may be utilized to produce the desired uniform magnetic field. The combined electric and magnetic fields influence the trajectory of the electron beam in the interaction region. Electrons which are not absorbed from the beam by the bounding electrodes comprising the delay line and sole electrode are collected by collector electrode 38.

Rigorous mathematical analysis as well as detailed experimental verification of the general electron-slow wave circuit interaction phenomenon in crossed field devices has yielded interesting infonnation which is of value in attempting to reduce spurious signal generation. In microwave devices having the elongated interaction region there exists a critical point along the interaction length where the RF level on the circuit drops rapidly to a zero value. In other words, a substantial amount of the charges strikes the circuit within the first portion of the interaction region. When there still remains a considerable interaction length beyond this critical point, which can be referred to as the point of beam saturation or collection, and the collector end of the circuit a still highly bunched electron beam can generate a signal which will propagate back into the first region to pull or lock onto the original oscillation frequency and thereby cause relaxation oscillation.

In FIG. 1 the first portion of the interaction region where the substantial frequency determining interaction occurs is designated as L and the solid line 40 is shown as curving toward the delay line 10. The remainder of the beam indicated by substantially rectilinear line 42 continues to the collector electrode 38. The second region which is believed to contribute to the spurious signal generation, particularly of the tunable sideband variety, covers the remainder of the interaction length and is designated I A computerized study has been undertaken of the RF amplitude level along an elongated interaction path to note the region of the greatest buildup of oscillations from low level to saturation. A mathematical model was utilized which serves as a generalization of the technique referred to in the article by J. Feinstein and G. S. Kino entitled The Large Signal Behavior of Crossed Field Traveling Wave Devices" in the Proceedings of the IRE, Vol. 45, (I957), pgs. l364l373. This work was substantiated by measurements along a slow wave circuit with maximum and minimum excursions of RF relative amplitude in the regions where spurious oscillations were observed in a particular tube. A computed idealized curve without spurious oscillations was also calculated. The range between maximum and minimum is approximately constant in the first half of the interaction region and falls linearly in the second half. In FIG. 2 the results of these studies are shown. Curves 44 and 46 are the maximum and minimum amplitude curves of the envelope of the pulse and curve 48 is the average value. The curve 50 is the computerized solution of output signals without spurious oscillations. It will be noted that an efficient device can be devised by operating over a shortened interaction region where the feedback or locking phenomenon is substantially reduced. This is particularly of interest in such devices for utilization in dual mode operation with high and low operating currents for CW or pulsed operation.

Referring now to FIGS. 3, 4 and 5, an embodiment of the invention is shown illustrative of selectively controlling the interaction length by varying the energy propagating circuit. In FIG. 3 a periodic slow wave circuit 52 of the interdigital delay line type is shown having individual opposing interleaved elements 54 and 56 extending respectively from parallel support bar members 58 and 60. At an intermediate point which may be calculated in accordance with optimum interaction lengths desired the circuit may be interrupted by selective control means such as semiconductor switching means to divide the overall interaction circuit into portions L and L In the exemplary embodiment element 54a is tenninated by a semiconductor device 62 connected through a resistor 64 to terminal 66 for connection to an external actuating pulse circuit. Similarly, element 56a is coupled to a semiconductor device 68, resistor 70 and terminal 72. The leads from the respective terminals 66 and 72 are insulated from the delay line support bars 58 and 60 by conventional dielectric or ceramic spacer means. In the illustrative embodiments a PIN diode may be employed .as the semiconductor switching means. When reverse biased with respect to ground the diode switching means providesan open circuit and no variation of the total interaction circuit length will occur. When a positive pulse from an appropriate source is applied to the terminals 66 and 72 the diode means become conducting and couple the resistors 64 and 70 of the appropriate delay line elements in the circuit as attenuators of RF energy. With suitable selection of appropriate resistors the propagation of waves along the line will be substantially prevented in a manner similar to lumped attenuators used in microwave propagation circuits. In the illustrative embodiment several resistors and switching diode means have been shown in order to provide for good broadband matching characteristics over a range of microwave frequencies.

With the switching diode means inactive the full interaction circuit L,+L is available, for example, the generation of continuous wave output signals where lower beam currents are conventionally employed. For the purposes of this description the term beam current is intended to refer to the total of the sole, collector as well as anode current. For pulsed operation, however, the higher currents are required. Substantially spurious-free operation can be realized when the interaction length is reduced to L The slow wave circuit switching means, then, substantially reduce the propagation of RF energy in the remainder of the interaction circuit and the exchange of energy with the electron beam. Frequency pulling and locking to cause relaxation oscillations with the frequency generated over the first interaction portion I. will be substantially avoided.

In FIGS. 4 and 5 another embodiment for interruption of the periodic slow wave circuit by selective central means is illustrated utilizing semiconductor switching means and attenuating signals by means of a transmission line directional coupler to divide the interaction lengths. An interdigital delay line of conventional interleave finger elements is indicated generally by the numeral 74 and extends in a direction perpendicular to the plane of the paper. A secondary delay line element 76 is disposed adjacent to and offset from the critical terminal area of interaction region portion L, by lossy material means 78, such as a ceramic material, appended to the tube back wall 80. In this embodiment four secondary delay line elements have been illustrated; however, this is a matter of choice dependent on the power levels to be attenuated and any number of elements between 1 and 10 will suffice in most applications. A semiconductor switching device 82 is coupled to the end of each secondary delay line element with a lead extending through a capacitive dielectric material 84 to terminal 136. A suitable dielectric material is referred to by the trademark MYLAR. The selective control diode means again will be normally reverse biased to permit the entire delay line 74 to be active. With the diode means rendered forward biased and conductive by an appropriate voltage pulse source short circuited secondary delay line elements are presented to the RF energy traversing the primary delay line circuit '74. The resultant high impedance by appropriate selection of the distance between the elements 76 and elements of the delay line 741 will provide for inductive coupling of energy to the elements 76. Such energy will be absorbed by the lossy material appended to the secondary delay line elements. The interaction length will thereby be again effectively reduced to the L, dimension. In lieu of the provision of the lossy material the secondary delay line element 76 may be coated with an attenuating material such as iron.

To assist in the practice of the invention, the distance for the interaction region portion L, generally averaged 45 percent of the total length with L having a value of 55 percent. These values are suggested and will vary dependent on the currents and operation modes involved in the different end uses. Further, selective control switching means may be supplied by external derived voltage sources as well as voltages derived from internal electrode sources such as the accelera-' tor where positive pulses are required.

In FIG. 6 another embodiment is now shown involving selective control of interaction lengths by electron beam interception. Operation at high as well as low currents in continuous and pulsed modes will be described. Delay line 88 is provided with terminals 90 and 92 for coupling to the output and termination means, respectively. An accelerator electrode M as well as cathode 96, grid 98 and collector electrode 101) may all be similar to the elements shown in FIG. 1. The interaction region is designated 102 and the magnetic field direction is indicated by circles and crosses 104 with the electric field perpendicularly disposed. The voltage sources for the accelerab ing electrode and grid electrode are designated 95 and 97. Another source 112 is connected to the cathode, thereby rendering this member negative with respect to ground. Delay line 118 is therefore rendered positive with respect to the cathode. In this embodiment the sole electrode is divided to provide a first section 106 and a second section 108. At a critical intermediate point along the interaction length a spurious control switching element 110 is provided. Sole electrode sections 106 and 111% are biased negatively with respect to cathode 96 by suitable sources 114 and 116. The collector electrode 11111 is at ground potential and therefore positive with respect to the cathode electrode.

As in the previous embodiments, it is desired for certain modes of operation to provide the entire interaction region L,+L which may now be 7 accomplished by means of interception of substantial portion of the electron beam by control element 1111. Without actuation of the control element 110 the beam trajectory is diagrammatically depicted by solid lines 118 and 120. With an appropriate pulse applied to control element 110 to alter the electric field potentials at the intermediate point the shortened interaction portion L, will result and the electron beam trajectory as indicated by dashed lines 122 and 124.

To accomplish the selective switching of the control element for electron beam interception a suggested circuit will now be described. A voltage source 126 having a designated value V,,, with a bypass capacitor 128 in shunt is coupled through an inductance coil 130 to the control element 110. A sensing coil element 132 is inductively coupled to the inductance coil 131) for the application of an actuating pulse having, illustratively, a waveform 134 from an external voltage source connected to terminals 136 and 1138. Again, as in the previous embodiments, internal derived voltage sources may also be utilized.

The contrdl element 110 it will be noted is negatively biased at some predetermined potential value V;,, by voltage source 126. For continuous wave interaction over the entire length of the interaction region L,+L and an absence of any switching pulse this negative voltage for low current operation can have a value of approximately I500 volts with respect to cathode electrode 96. For higher current operation the supply may provide a positive potential with respect to the cathode having a value of, for example, 400 volts. In this mode of operation the electron beam will be represented by the solid lines 116 and 120. For the generation of pulsed output signals both the low and high current conditions will have the same values for voltage supply 126; however, the interaction lengths will now be reduced to a dimension L, by the application of a suitable switching pulse through the sensing coil 132 to coil to alter the biasing on the control element 110. For low current conditions a positive switching pulse added to the negative potential will render the element 110 less negative with respect to cathode to facilitate interception of the beam at this point and absorption of a substantial portion thereof by the element 110. For high current conditions a positive voltage induced on the already positive potential will result in beam col lection. The circuit herein disclosed is intended as a guide and many other circuit arrangements will readily occur to those skilled in the art which will render the control element in the proper attitude for interception of the beam to thereby shorten the beam trajectory and interaction regions.

In FIG. 7 the control of the propagation characteristics may be effected in a segmented sole electrode configuration. To aid in the understanding of this embodiment of the invention structure similar to that shown and described in FIG. 6 has been similarly numbered. The sole electrode in this embodiment is divided into any number of appropriate segments designated illustratively S, and S The first segment is suitably dimensioned to provide the interaction. length L, and is biased by a supply 1411) having a potential V5,. The second segment 5 is biasedby a vpltage source 142 hayi 1g a potential VSz. A bypass capacitor 144 may also be connected in shunt across supply M2. An inductance 146 is coupled to a coil 14% for inducing a voltagediiferentialin sole segment 5, from a voltage switching pulse having an illustrative waveform 1511 derived externally from a source connected to terminals 152 and 1541. An internal derived switch pulse may also be provided in this embodiment as was stated with respect to the embodiments hereinbefore described.

Operation to selectively alter the propagation and electrical characteristics is now provided by substantially altering the beam velocity in the region of the sole 5,. By a substantial dropping of the voltages in this region effectively little beamto-circuit coupling or interaction takes place because of the sharp reduction in beam velocity to a nonsynchronous condi tion. For full length interaction operation such as that desired for continuous wave outputs and normal current conditions the electron beam has a trajectory represented by solid lines 156 and 156. With the drop in voltage in sole segment 8;, and another set of conditions arises and the trajectory is represented by dashed lines 160 and 162. It will be noted that in the downstream portion adjacent sole segment S the beam is not intercepted as in FIG. 6. Further, the wave propagation circuit is not divided as in FIG. 5 but rather distortion of the beam results 'as shown by line 162. With appropriate circuitry this condition can be derived by having both voltages VS, and VS from voltage supplies 1410 and 142 essentially the same for interaction over the total length of the interaction iegion. Upon application of the switching pulse, however, through coil M8 the first segment S, is held at a negative potential while the potential V8 differs sufficiently to yield the nonsynchronous condition. In this operation mode a highly bunched electron beam 'will be present in the portion L during the pulsed condition which will permit operation of the tube over the total interaction length when the continuous wave signals operation mode is resumed.

Referring now to FIGS. 6 and '9, another embodiment of the invention is shown for reduction of spurious output signals by selectively electronically controlling the interaction region electrical and propagation characteristics. In the previous embodiments control of the propagation circuit, interception of the electron beam and substantial alteration of the beam trajectory in the downstream portion by a segmented sole electrode were noted. In the present embodiment the phase of the RF energy propagating along the periodic slow wave circuit will be altered to thereby alter the beam-circuit exchange of energy over a predetermined portion of the interaction region. Again, similar structure described in FIGS. 6 and 7 have been similarly numbered. In addition, for the sake of clarity the voltage supplies and circuit connections for biasing the electrodes have been omitted since they were previously described, particularly with reference to FIG. 1. The sole electrode in this embodiment is designated 164 and the electron beam trajectory is indicated by solid line 166. At the critical point along the delay line circuit a semiconductor diode switched microwave phase shifter 168 is coupled to the delay line elements. An input switching pulse from an external source having an illustrative waveform 170 is coupled to terminals 172 and 174 to electronically actuate the phase shifter. An appropriate adjustment of the phase between the two portions L, and L for a particular mode of operation will be introduced into the circuit. The inserted phase shift may vary dependent upon desired operating conditions; however, in most instances a 180 value will suffice. The optimum lengths of portions L and L will again be selected as in the previous embodiments to provide substantially spurious free output signals. With the downstream portion L out-of-phase with the overall circuit, interaction will be effective only over the initial or L portion where the beam velocity and circuit characteristics are synchronous. For total overall interaction both regions will be in phase to yield the output signal.

In FIG. 9 curve 176 indicates the phase characteristics and RF level in portions L and L, without introduction of a phase adjustment. Dashed curve 178 indicates the RF energy phase characteristics with the appropriate phase shift now introduced into the circuit. The contributions to the output signal of the two portions will add constructively. The circuit for switching the desired phase shift is believed to be within the realm of knowledge of skilled artisans and has not been further elaborated on in this description. The phase shifter means will comprise a ferromagnetic material controlled by electromagnetic means such as a solenoid for altering the phase characteristics of transmitted wave energies.

in all of the previously described embodiments an M-type backward wave oscillator device has been illustrated. The invention will also be equally applicable to O-type backward wave oscillators as well as any other devices utilizing beamcircuit interaction for amplification or generation of microwave signals. It is als understood that numerous modifications, alterations and variations will readily occur to those skilled in the art for electronically actuating the interaction controlling elements to interrupt and vary energy propagation characteristics. It is intended, then, that all matters shown and described herein be interpreted broadly as illustrative of the scope of the invention defined in the appended claims and not in a limiting sense.

lclaim:

l. A traveling wave electron interaction device comprising:

means for propagating electromagnetic wave energy along a path;

electrode means spaced from and substantially coextensive with said propagating means to define therebetween an interaction region;

means for providing an electron beam within said interaction region in energy exchanging relation with electromagnetic waves; and

electronically actuated selective control means disposed at a predetermined critical point intermediate to the ends of said path to provide at least two interaction regions with one active and the other inactive with said electron beam interacting in energy exchanging relationship with principally the active region when said control means are actuated.

2. A traveling wave electron interaction device comprising:

slow wave circuit means for propagating electromagnetic wave energy;

electrode means spaced from and substantially coextensive with said circuit means to define therebetween an interaction region;

means for providing an electron beam within said region in energy exchanging relation with electromagnetic waves on said circuit; and

electronically actuated selective control means disposed at a predetermined critical point intermediate to the ends of said circuit to provide discrete active and inactive portions of said interaction region with said active region having a predetermined length oriented upstream with respect to the travel of said electron beam.

3. A traveling wave electron interaction device comprising:

a slow wave structure for propagating electromagnetic wave energy;

a sole electrode spaced from and coextensive with said slow wave structure to define therebetween an interaction region;

an electron source disposed at one end of said interaction region for directing a beam of electrons within said region in energy exchanging relation with electromagnetic waves;

means for establishing mutually perpendicular electric and magnetic fields within said region;

electronically actuated selective control means disposed at the point of maximum beam saturation along said interaction region; and

said control means when actuated effectively rendering one fields of said interaction region inactive by substantially altering its electrical characteristics to substantially inhibit any further exchange of energy between said beam and propagated waves beyond this point.

4. A traveling electron interaction device comprising:

a slow wave structure for propagating electromagnetic wave energy;

a sole electrode spaced from and substantially coextensive with said slow wave structure to define therebetween an interaction region;

an electron source for directing a beam of electrons within said region to exchange energy with electromagnetic waves;

means for establishing mutually perpendicular electric and magnetic fields within said region;

electronically actuated selective control means disposed at a predetermined critical point along said slow wave structure to interrupt and vary the energy propagating characteristics; and i said control means when actuated electrically dividing said slow wave structure into an active portion adjacent to said electron source and an inactive portion both of predetermined lengths with interaction confined principally to energy exchange relationship with said active portion for pulsed wave operation with relatively high beam currents and continuous wave operation with low beam currents when said control means are deactivated with interaction confined to both portions.

5. A traveling wave device according to claim 4 wherein said slow wave structure comprises an interdigital delay line having a plurality of interleaved conductive elements.

6. A traveling wave device according to claim 5 wherein said control means are coupled to at least one of said delay line elements. I

7. A traveling wave device according to claim 6 wherein said control means comprise semiconductor means actuated by electrical pulse signals.

8. A traveling wave device according to claim 4 wherein said control means are disposed laterally from said slow wave structure at an intermediate point along said interaction region to couple and absorb energy to vary the energy propagating characteristics.

9. A traveling wave device according to claim 8 wherein said slow wave structure comprises an interdigital delay line 9 having a plurality of interleaficonductive elements and said control means comprise at least one other conductive element inductively coupled to said delay line, said inductively coupled element being connected to an electromagnetic energy absorbing material.

10. A traveling wave device according to claim 9 wherein said control means comprise semiconductor means actuated by electrical pulse signals.

11. A traveling wave electron interaction device comprismg:

a slow wave structure for propagating electromagnetic wave energy;

electrode means spaced from and substantially coextensive with said slow wave structure to define therebetween an interaction region;

an electron source for directing a beam of electrons within said region to exchange energy with electromagnetic waves;

means for establishing mutually perpendicular electric and magnetic fields within said region;

selective control means disposed at a predetermined critical point along said coextensive electrode means; and

said control means being adapted to provide an electrical potential sufi'rcient to intercept a substantial portion of said electron beam and electrically divide said interaction region into active and inactive portions with said active region being closest to said electron source.

12. A traveling wave electron interaction device according to claim 11 wherein said control means are actuated by electrical signals inductively coupled from a source of voltage pulses.

13. A traveling wave electron interaction device comprismg:

a slow wave structure for propagating electromagnetic wave energy;

a sole electrode spaced from and substantially coextensive with said slow wave structure to define therebetween an interaction region;

said sole electrode being electrically divided into two segments;

an electron source for directing a beam of electrons within said region to exchange my when the velocity of said electrons is in synchronous relationship with the phase of electromagnetic waves;

means for establishing mutually perpendicular electric and magnetic fields within said region; and

selectively actuated circuit means for biasing one of said sole electrode segments at an electric field potential to substantially alter the electron beam velocity at the point of maximum electron beam bunching and establish a nonsynchronous relationship in the remainder of the interaction region beyond this point whereby energy exchange is effectively restricted the the region bounded by the remaining sole electrode segment.

14. A traveling wave electron interaction device according to claim 13 wherein said selective actuating means comprise electrical signals inductively coupled from a source of voltage pulses.

15. A traveling electron interaction device comprising:

a slow wave structure for propagating electromagnetic wave energy;

a sole electrode spaced from said slow wave structure and defining therebetween an interaction region;

an electron source for directing a beam of electrons within said region to exchange energy when the velocity of said electrons is in synchronous relationship with the phase of electromagnetic waves;

means for establishing mutually perpendicular electric and magnetic fields within said region;

electronically actuated selective control means disposed at the point of maximum beam saturation to substantial alter the slow wave structure propagating characteristics; and said control means when actuated electrically dividmg said my UNlTED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. ,3 573,540 Dated April 6, 1971 Inventor (5) John M Osepchuk It is certified that error appears in the abode-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 8, Line 26 (Claim 3) After insert --and-- Col. 8, Line 29 (Claim 3) After delete "and" Col. 8, Lines 30, 31 (Claim 3) After "one" delete "fields" and insert --portion-'- Col. 8, Line 45 (Claim 4) After insert --and-- Col. 8, Line 49 (Claim 4 After delete "and" Col. 8, Line 54 (Claim 4) After "energy" delete "exchange" and insert --exchangi C01. 9, Line 20 (Claim 11) After insert --and-- Col. 9, Line 22 (Claim 11) After delete "and" Col. 10, Line 28 (Claim 15) After insert -and C01. 10, Line 30 (Claim 15) After "to" delete "substantial" and insert --substa.nti

Col. 10, Line 31 (Claim 15) After delete "and" L Col. 10, Line 33 (Claim 15) After "into" delete "a" and insert --an-- -Signed and sealed this 5th day of October 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTCCHALK Attesting Officer Acting Commissioner of Pate 

1. A traveling wave electron interaction device comprising: means for propagating electromagnetic wave energy along a path; electrode means spaced from and substantially coextensive with said propagating means to define therebetween an interaction region; means for providing an electron beam within said interaction region in energy exchanging relation with electromagnetic waves; and electronically actuated selective control means disposed at a predetermined critical point intermediate to the ends of said path to provide at least two interaction regions with one active and the other inactive with said electron beam interacting in energy exchanging relationship with principally the active region when said control means are actuated.
 2. A traveling wave electron interaction device comprising: slow wave circuit means for propagating electromagnetic wave energy; electrode means spaced from and substantially coextensive with said circuit means to define therebetween an interaction region; means for providing an electron beam within said region in energy exchanging relation with electromagnetic waves on said circuit; and electronically actuated selective control means disposed at a predetermined critical point intermediate to the ends of said circuit to provide discrete active and inactive portions of said interaction region with said active region hAving a predetermined length oriented upstream with respect to the travel of said electron beam.
 3. A traveling wave electron interaction device comprising: a slow wave structure for propagating electromagnetic wave energy; a sole electrode spaced from and coextensive with said slow wave structure to define therebetween an interaction region; an electron source disposed at one end of said interaction region for directing a beam of electrons within said region in energy exchanging relation with electromagnetic waves; means for establishing mutually perpendicular electric and magnetic fields within said region; electronically actuated selective control means disposed at the point of maximum beam saturation along said interaction region; and said control means when actuated effectively rendering one fields of said interaction region inactive by substantially altering its electrical characteristics to substantially inhibit any further exchange of energy between said beam and propagated waves beyond this point.
 4. A traveling electron interaction device comprising: a slow wave structure for propagating electromagnetic wave energy; a sole electrode spaced from and substantially coextensive with said slow wave structure to define therebetween an interaction region; an electron source for directing a beam of electrons within said region to exchange energy with electromagnetic waves; means for establishing mutually perpendicular electric and magnetic fields within said region; electronically actuated selective control means disposed at a predetermined critical point along said slow wave structure to interrupt and vary the energy propagating characteristics; and said control means when actuated electrically dividing said slow wave structure into an active portion adjacent to said electron source and an inactive portion both of predetermined lengths with interaction confined principally to energy exchange relationship with said active portion for pulsed wave operation with relatively high beam currents and continuous wave operation with low beam currents when said control means are deactivated with interaction confined to both portions.
 5. A traveling wave device according to claim 4 wherein said slow wave structure comprises an interdigital delay line having a plurality of interleaved conductive elements.
 6. A traveling wave device according to claim 5 wherein said control means are coupled to at least one of said delay line elements.
 7. A traveling wave device according to claim 6 wherein said control means comprise semiconductor means actuated by electrical pulse signals.
 8. A traveling wave device according to claim 4 wherein said control means are disposed laterally from said slow wave structure at an intermediate point along said interaction region to couple and absorb energy to vary the energy propagating characteristics.
 9. A traveling wave device according to claim 8 wherein said slow wave structure comprises an interdigital delay line having a plurality of interleaved conductive elements and said control means comprise at least one other conductive element inductively coupled to said delay line, said inductively coupled element being connected to an electromagnetic energy absorbing material.
 10. A traveling wave device according to claim 9 wherein said control means comprise semiconductor means actuated by electrical pulse signals.
 11. A traveling wave electron interaction device comprising: a slow wave structure for propagating electromagnetic wave energy; electrode means spaced from and substantially coextensive with said slow wave structure to define therebetween an interaction region; an electron source for directing a beam of electrons within said region to exchange energy with electromagnetic waves; means for establishing mutually perpendicular electric and magnetic fields within said region; selective control means disposed at a predetermined critical poiNt along said coextensive electrode means; and said control means being adapted to provide an electrical potential sufficient to intercept a substantial portion of said electron beam and electrically divide said interaction region into active and inactive portions with said active region being closest to said electron source.
 12. A traveling wave electron interaction device according to claim 11 wherein said control means are actuated by electrical signals inductively coupled from a source of voltage pulses.
 13. A traveling wave electron interaction device comprising: a slow wave structure for propagating electromagnetic wave energy; a sole electrode spaced from and substantially coextensive with said slow wave structure to define therebetween an interaction region; said sole electrode being electrically divided into two segments; an electron source for directing a beam of electrons within said region to exchange energy when the velocity of said electrons is in synchronous relationship with the phase of electromagnetic waves; means for establishing mutually perpendicular electric and magnetic fields within said region; and selectively actuated circuit means for biasing one of said sole electrode segments at an electric field potential to substantially alter the electron beam velocity at the point of maximum electron beam bunching and establish a nonsynchronous relationship in the remainder of the interaction region beyond this point whereby energy exchange is effectively restricted the the region bounded by the remaining sole electrode segment.
 14. A traveling wave electron interaction device according to claim 13 wherein said selective actuating means comprise electrical signals inductively coupled from a source of voltage pulses.
 15. A traveling electron interaction device comprising: a slow wave structure for propagating electromagnetic wave energy; a sole electrode spaced from said slow wave structure and defining therebetween an interaction region; an electron source for directing a beam of electrons within said region to exchange energy when the velocity of said electrons is in synchronous relationship with the phase of electromagnetic waves; means for establishing mutually perpendicular electric and magnetic fields within said region; electronically actuated selective control means disposed at the point of maximum beam saturation to substantial alter the slow wave structure propagating characteristics; and said control means when actuated electrically dividing said slow wave structure into a active portion adjacent said electron source and an inactive portion downstream thereof to introduce substantially out-of-phase characteristics in waves propagating in said inactive portion and substantially confine the in-phase energy exchanging relationship principally to said active portion.
 16. A traveling wave electron interaction device according to claim 15 wherein said control means comprise a semiconductor actuated phase shifter. 